1. Field of the Invention
The present invention relates to a flat cathode ray tube (CRT), and more particularly, to a tension mask frame assembly having an improved frame for supporting a tension mask having a color distinction function.
2. Description of the Related Art
In color cathode ray tubes (CRTs), three electron beams emitted from an electron gun land on red, green and blue fluorescent materials on a fluorescent film, which is formed on the screen surface of a panel, through electron beam passing holes of a shadow mask which has a color distinction function, and excite the fluorescent materials, whereby a picture is formed.
Recent color CRTs pursue a flat screen surface to widen the viewing angle of a picture and prevent distortion of a picture, which requires flattening of a mask which is installed within a CRT and has a color distinction function. The mask becomes an obstacle in fabricating a completely-flat CRT.
FIG. 1 shows an example of a tension mask frame assembly of a flat CRT.
As shown in FIG. 1, the tension mask frame assembly includes a frame 10 and a flat tension mask 20. The frame 10 includes first and second support members 11 and 12 which are parallel, and first and second elastic members 13 and 14, the ends of which are fixed to the first support member 11 and the second support member 12, to maintain an equal distance between the first and second support members 11 and 12. The flat tension mask 20 has facing longer sides which are welded to the support members 11 and 12 so that tension is applied to the support members 11 and 12, and has rows of slits 22 separated by strips 21.
The flat strips 21 are connected to each other at predetermined intervals by tie bars 23, such that the slits 22 are formed.
In the tension mask frame assembly, the flat tension mask 20 is supported by the first and second support members 11 and 12 in a state where a great tensile stress is applied to the flat tension mask 20, such that a non-uniform tensile stress is applied to areas on the first and second support members 11 and 12.
That is, in order to weld the flat tension mask 20 to the first and second support members 11 and 12 of the frame 10, the firsts and second support members 11 and 12 are pressurized from both sides and are displaced in a facing direction, whereby the first and second elastic members 13 and 14 are pressurized and elastically deformed. In this state, both longer sides of the flat tension mask 20 are welded to the first and second support members 11 and 12, and pressure to the first and second support members 11 and 12 are eliminated. Here, the restoring force of the first and second support members 11 and 12 is different at areas, which are supported by the first and second elastic members 13 and 14, and at their center areas.
The difference in restoring force is shown as a difference in tensile stress applied to each strip on a tension mask. As shown in graph A of FIG. 2, portions of the tension mask 20 which are supported by the first and second elastic members 13 and 14 are subjected to much stress, while the strips 21 farther away from the portions supported by the first and second elastic members 13 and 14 are subjected to less tensile stress.
Due to the difference in tensile stress, the tension mask 20 cannot absorb a sufficient amount of thermal expansion at the center portion upon thermal expansion by an electron beam, and the tension mask 20 is partially shrunk or expanded by a non-uniform tension, so that slits 22 traversed by electron beams are deformed. The deformation of the slits 22 hinders accurate landing of an electron beam emitted from an electron gun in a CRT to a fluorescent film.
Therefore, the tension mask passes a different number of electron beams through slits in different areas, and thus cannot obtain a uniform resolution of a picture at different areas. Also, a portion of the tension mask, to which a relatively small tensile stress is applied, vibrates severely even with a small external impact, thus causing screen jitter.
To solve the above problem, an objective of the present invention is to provide a tension mask frame assembly for a flat CRT having an improved color distinction function of an electron beam, in which the structural intensity of a support member constituting a frame is improved to prevent partial distortion of the tension mask due to the non-uniformity of a tensile stress applied to the tension mask fixed to the support member.
To achieve the above objective, a flat tension mask frame assembly according to an aspect of the present invention is provided, including: a frame having first and second support members which are separated from each other by a predetermined distance, and have fixing portions and flange portions which are bent inwardly from the fixing portions and become narrower from the center portion to both ends of the flange portions, and at least two elastic members each fixed at both ends to the first and second support members for supporting the support members; and a tension mask, facing edges of which are fixed to the fixing portions of each of the first and second support members in a state where a tensile stress has been applied to the facing edges.
To achieve the above objective, a flat tension mask frame assembly according to another aspect of the present invention is provided, including: a frame having first and second support members which are separated from each other by a predetermined distance, and have fixing portions which are bent at predetermined curvatures outwardly in an opposite direction, and flange portions which are bent inward at predetermined angles from the fixing portions while becoming wider from the support portions of the elastic members to the center portion, and at least two elastic members each fixed at both ends to the first and second support members for supporting the support members; and a tension mask, facing edges of which are fixed to the fixing portions of each of the first and second support members in a state where a tensile stress has been applied to the facing edges.